I wonder how in your opinion atheism enters in the picture? My first guess (of your reference) is that certain religions frighten people into remaining in a marriage they would otherwise not be in. My second guess is that religion fills a social glue role by virtue of getting people together to worship or do other community things.
In my own opinion, part of the problem is that we are not atheist enough, and we still believe in the god-mandated union of a man and a woman, properly enclosed by walls, to bring forth children, as the only way worth living. Yes, there are pockets of resistance to the idea, but too little and too late. By far and large all parents out there are pressing their children to marry and have kids, so that there are grandchildren to fill those golden years. And there is mass media of course, which by far and large does the same. But I suspect that, left to their own devices, a lot of young people may choose to stick to their childhood friends of their same sex or otherwise, and employ one of the myriad ways humans can achieve sexual fulfillment. And since I'm on the topic, our species had sex for bonding long before it had religion, language, and the Internet. It's a pity that after the agricultural revolution and the newly found greed for land, God declared that technology suitable only for establishing property rights and for growing the military might of the tribe.